Alpha-olefin oligomers and their use as hydraulic fluids and synthetic lubricants (synlubes) are well known. U.S. Pat. No. 2,937,129 reports the oligomerization of C.sub.5-14 .alpha.-olefins using a dialkyl peroxide catalyst to make a synlube. U.S. Pat. No. 3,113,167 describes an .alpha.-olefin oligomer process using a titanium halide and an aluminum compound as the oligomerization catalyst.
The preferred catalysts for making .alpha.-olefin oligomers are Friedel Crafts catalysts such as BF.sub.3 as disclosed in U.S. Pat. No. 3,149,178. Optimum properties are obtained starting with 1-decene although mixtures of .alpha.-olefins have been used, cf. U.S. Pat. No. 3,330,883.
The preferred Friedel Crafts catalyst is BF.sub.3. Pure BF.sub.3 is not an effective oligomerization catalyst. A small amount of polar compound is necessary as a promoter. U.S. Pat. No. 3,382,291 describes the use of alcohol promoters such as decanol. Other reported promoters are modenite (hydrogen form), water, phosphoric acid, fatty acids (e.g. valeric acid), ketones, organic esters, ethers, polyhydric alcohols, silica gel and the like.
The most common catalyst, BF.sub.3, can present a disposal problem. Various methods have been devised for removing BF.sub.3 from an oligomerization reaction to achieve an environmentally acceptable result. Vogel et al. U.S. Pat. No. 4,454,366 and U.S. Pat. No. 4,384,162 describe the use of polyvinyl alcohol to remove BF.sub.3 from an oligomerization reaction. Vogel et al. U.S. Pat. No. 4,433,197 contacts the reaction product with silica to remove the BF.sub.3. Morganson et al. U.S. Pat. No. 4,429,177 and Madgavkar et al. U.S. Pat. No. 4,213,001 and U.S. Pat. No. 4,308,414 use silica as an absorbant for BF.sub.3 in an oligomerization process. Madgavkar et al. U.S. Pat. No. 4,394,296 describe the use of wet silica as a co-catalyst with BF.sub.3 in an oligomer process. The silica can be filtered off and recycled as the catalyst. Madgavkar et al. U.S. Pat. No. 4,263,467 remove BF.sub.3 by trickling the reaction product over an inert metallic or ceramic bed whereby the BF.sub.3 is said to evaporate and can be recovered.
From this it can be seen that a great deal of effort has gone into developing a method for removing BF.sub.3 from an olefin oligomerization process in an environmentally safe manner.